Electric storage device protection apparatus, electric storage apparatus, starter battery, and method of protecting electric storage device

ABSTRACT

An electric storage device protection apparatus includes switches arranged between an electric device and an electric storage device and connected in parallel to each other, a rectifier component connected in series to one of the switches between a pair of common connection points of the switches, and a controller. The controller is configured to make the switch connected to the rectifier component to be in the open state when determining that a voltage of the electric storage device is within a reference range, and make the switch that is connected to the rectifier component to be in the closed state and make another one of the switches to be in the open state when determining that a voltage of the electric storage device becomes outside the reference range due to a current flowing in a reverse direction of the rectifier component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application No.2013-92686 filed on Apr. 25, 2013. The entire contents of the priorityapplication are incorporated herein by reference.

FIELD

Technologies described herein relates to a technology for monitoring astate of an electric storage device.

BACKGROUND

Conventionally, there has been a current control circuit that restrictsoccurrence of overcharge or overdischarge of a secondary battery (e.g.JP-A-2013-018464). Such a current control circuit includes a circuitincluding a first diode and a first switch that are connected to eachother in series and a circuit including a second diode and a secondswitch that are connected to each other in series, and such two circuitsare connected to each other in parallel. The first diode is connected soas to block a current flowing in a discharge direction that dischargeselectric power from the secondary battery, and the second diode isconnected so as to block a current flowing in a charge direction thatcharges the secondary battery with electric power.

In the current control circuit, if the first switch is in a closed stateand the second switch is in an open state, the current flowing in thedischarge direction is blocked by the first diode, and accordingly, thesecondary battery is less likely to become in the overdischarge state.In the current control circuit, if the first switch is in the open stateand the second switch is in the closed state, the current flowing in thecharge direction is blocked by the second diode, and accordingly, thesecondary battery is less likely to become in the overcharge state.

SUMMARY

The following presents a simplified summary of the invention disclosedherein in order to provide a basic understanding of some aspects of theinvention. This summary is not an extensive overview of the invention.It is intended to neither identify key or critical elements of theinvention nor delineate the scope of the invention. Its sole purpose isto present some concepts of the invention in a simplified form as aprelude to the more detailed description that is presented later.

In the above-described technology, the current always flows through oneof the first diode and the second diode regardless of whether thesecondary battery is in the overdischarge state or the overcharge state.Therefore, the diode may be heated excessively.

This specification describes a technology for restricting occurrence ofheating by a rectifier component such as the diode and less causing theelectric storage device such as the secondary battery to become in theovercharge state or the overdischarge state.

An electric storage device protection apparatus described in thisspecification includes switches arranged between an electric device andan electric storage device and connected in parallel to each other, andeach of which being configured to be switched to be in an open state anda closed state, a rectifier component connected in series to one of theswitches between a pair of common connection points of the switches, anda controller. The controller is configured to perform a first process tomake the one of the switches that is connected to the rectifiercomponent to be in the open state when determining that the electricstorage device is in a first state where a voltage of the electricstorage device is within a reference range, and perform a second processto make the one of the switches that is connected to the rectifiercomponent to be in the closed state and make another one of the switchesto be in the open state when determining that the electric storagedevice is in a second state where a voltage of the electric storagedevice becomes outside the reference range due to a current flowing in areverse direction of the rectifier component.

According to the above configuration, heating by the rectifier componentis less likely to occur and an electric storage device is less likely tobecome in an overcharge state or an overdischarge state.

BRIEF DESCRIPTION OF DRAWINGS

The foregoing and other features of the present invention will becomeapparent from the following description and drawings of an illustrativeembodiment of the invention in which:

FIG. 1 is a block diagram of an electric storage apparatus according toone embodiment;

FIG. 2 is a graph illustrating a relationship between an OCV and a SOC;

FIG. 3 is a graph illustrating a cell current and a cell voltageaccording to elapsed time when each cell is charged with a constantvoltage;

FIG. 4 is a flowchart illustrating a secondary battery protectionprocess;

FIG. 5 is a flowchart illustrating an overcharge protection process;

FIG. 6 is a transition diagram illustrating switching of a switch in theovercharge protection process;

FIG. 7 is a flowchart illustrating an overdischarge protection process;and

FIG. 8 is a circuit diagram illustrating a connection state of athree-points switching relay.

DESCRIPTION OF EMBODIMENTS

An electric storage device protection apparatus described in thisspecification includes switches arranged between an electric device andan electric storage device and connected in parallel to each other, andeach of which being configured to be switched to be in an open state anda closed state, a rectifier component connected in series to one of theswitches between a pair of common connection points of the switches, anda controller. The controller is configured to perform a first process tomake the one of the switches that is connected to the rectifiercomponent to be in the open state when determining that the electricstorage device is in a first state where a voltage of the electricstorage device is within a reference range, and perform a second processto make the one of the switches that is connected to the rectifiercomponent to be in the closed state and make another one of the switchesto be in the open state when determining that the electric storagedevice is in a second state where a voltage of the electric storagedevice becomes outside the reference range due to a current flowing in areverse direction of the rectifier component.

With this apparatus, as long as it is not determined that the electricstorage device is in the second state, the path of a current flowing viathe rectifier component is not formed, and this restricts occurrence ofheating by the rectifier component. When it is determined that theelectric storage device is in the second state, the path of a currentflowing via the rectifier component is formed. Therefore, the currentflows only in the discharge direction, and accordingly, the electricstorage device is less likely to be in the overcharge state.

In the electric storage device protection apparatus, the switches mayinclude a first switch and a second switch, and the first switch may bearranged between the electric device and the electric storage device andswitched between the open state and the closed state, and the secondswitch may be connected in parallel to the first switch between theelectric device and the electric storage device and switched between theopen state and the closed state. The rectifier component may beconnected in series to the second switch between the pair of commonconnection points of the first switch and the second switch. Thecontroller may be configured to make at least the first switch to be inthe closed state when determining that the electric storage device is inthe first state, and make the first switch to be in the open state andmake the second switch to be in the closed state when determining thatthe electric storage device is in the second state.

With this electric storage device protection apparatus, when theelectric storage device is in the first state, at least the first switchbecomes in the closed state. The first switch is not connected in seriesto the rectifier component, and therefore, compared to a configurationwhere the first switch is connected in series to the rectifiercomponent, occurrence of heating by the rectifier component isrestricted. When the electric storage device is in the second state, thefirst switch becomes in the open state and the second switch becomes tobe in the closed state. Accordingly, a current flowing in the reversedirection of the rectifier component is blocked by the rectifiercomponent. Therefore, the electric storage device is less likely tobecome in the overcharge state by the current flowing in the reversedirection of the rectifier component.

In the electric storage device protection apparatus, the electric devicemay include a charger and a load, and the first switch, the secondswitch, and the rectifier component may be connected to a common currentpath commonly arranged between the charger and the electric storagedevice and between the load and the electric storage device.

With this electric storage device protection apparatus, by performingthe second process, the first switch becomes in the open state and thesecond switch becomes in the closed state. Accordingly, the current paththrough which the current flows in the forward direction of therectifier component is less likely to be blocked.

In the electric storage device protection apparatus, the controller maybe configured to make the second switch to be in the closed state firstand thereafter make the first switch to be in the open state in thesecond process.

With this electric storage device protection device, during theperformance of the second process, both of the first switch and thesecond switch are not in the open state at the same time, and therefore,the current flowing in the forward direction of the rectifier componentis not blocked for a moment.

In the electric storage device protection apparatus, the controller maybe further configured to determine whether the electric storage deviceis in a third state where the voltage of the electric storage devicebecomes outside the reference range due to a current flowing in aforward direction of the rectifier component, and perform a thirdprocess to make the first switch and the second switch to be in the openstate when determining that the electric storage device is in the thirdstate.

With this electric storage device protection apparatus, when theelectric storage device is in the third state, the first switch and thesecond switch become to be in the open state. Accordingly, the electricstorage device is less likely to become in the overdischarge state bythe current flowing in the forward direction of the rectifier component.

The electric storage device protection apparatus may further include adischarger connected in parallel to the electric storage device andconfigured to be switched between a discharge state where electric poweris discharged from the electric storage device and a stop state wheredischarge is stopped. In the electric storage device protectionapparatus, the rectifier component may be connected to the second switchso as to block a current flow that charges the electric storage device,and the controller may be further configured to perform the stop processto make the discharger in the stop state when determining that theelectric storage device is in the first state, and perform the dischargeprocess to make the discharger in the discharge state when determiningthat the electric storage device is in the second state.

With this electric storage device protection apparatus, when theelectric storage device is in the second state, the discharger becomesin the discharge state and discharges electric power from the electricstorage device. Therefore, compared to a configuration without includingthe discharger, the electric storage device is further less likely tobecome in the overcharge state by the current flowing in the reversedirection of the rectifier component.

In the electric storage device protection apparatus, the controller maybe further configured to make the second switch to be in the open statein the first process.

With this electric storage device protection apparatus, the currentflowing through the rectifier component is blocked and this surelyrestricts occurrence of heating by the rectifier component.

An electric storage apparatus described in this specification includesan electric storage device and the electric storage device protectionapparatus.

The electric storage device may include a positive electrode materialincluding a lithium compound containing an iron component and a specificlithium compound as a positive electrode active material, the specificlithium compound providing an open circuit voltage greater than an opencircuit voltage provided by the lithium compound containing the ironcompound included as the positive electrode active material, and theopen circuit voltage being obtained in a flat region where a change rateof the open circuit voltage per a state of charge unit is small.

Accordingly, compared to a configuration without adding a high voltageadaption material, the change ratio reduces in a region where the changeratio of the open circuit voltage per unit charge state is great. Thisrestricts occurrence of abrupt change of the OCV in a region that thecharge state is close to a full charge state.

The invention described in this specification may be achieved in variousmethods such as a controller, a control method, a computer programachieving functions of the controller or the control method, or arecording medium storing the computer program.

First Embodiment

A first embodiment will be described with reference to FIGS. 1 to 7.

As illustrated in FIG. 1, an electric storage apparatus 1 of the presentembodiment is mounted to a vehicle such as an engine vehicle and ahybrid vehicle and is a starter battery that supplies electric power toa starter 3 to start an engine 2. The electric storage apparatus 1supplies electric power to an in-vehicle device 4 such as head lights,an audio system or a security system. The electric storage apparatus 1is charged with electric power that is generated by an alternator 5according to rotation of the engine 2. The starter 3 and the in-vehicledevice 4 are examples of loads to which electric power is supplied fromthe electric storage apparatus 1. The alternator 5 is one example of acharger that charges the electric storage apparatus 1 or a powergenerator. The loads and the charger are examples of electric devices.

Configuration of Electric Storage Apparatus

The electric storage apparatus 1 includes an assembled battery 11, acircuit switch 12, and a battery management system (BMS) 13. Theassembled battery 11 is one example of the electric storage device andincludes a plurality of cells CN that are connected in series to eachother. Each of the cells CN is a secondary battery that is rechargeable.Specifically, each of the cells CN is a lithium ion secondary batterythat includes a negative electrode including a graphite-based materialas a negative electrode active material and a positive electrodeincluding an iron phosphate-based material as the positive electrodeactive material. In FIG. 1 and in the following description, theassembled battery 11 includes four cells C1 to C4. A combination of thecircuit switch 12 and the BMS 13 configure one example of the electricstorage device protection apparatus.

The assembled battery 11 is connected to the starter 3, the in-vehicledevice 4 and the alternator 5 via the circuit switch 12. The circuitswitch 12 is connected between the alternator 5 and the assembledbattery 11 and between the in-vehicle device 4 and the assembled battery11. The circuit switch 12 is arranged on a common current path throughwhich the discharge current flows from the assembled battery 11 to thestarter 3 and the charge current flows from the alternator 5 to theassembled battery 11.

The circuit switch 12 includes a first relay 12A, a second relay 12B,and a diode D, and the first relay 12A and the second relay 12B areconnected to each other in parallel. The first relay 12A is acontact-type relay (a mechanical switch) including a contact point and amagnetic coil, for example. If receiving an open command signal from acontroller 22 that will be described later, the first relay 12Amechanically opens the contact point by an electromagnetic action (anopen state or an OFF state). If receiving a close command signal fromthe controller 22 that will be described later, the first relay 12Amechanically closes the contact point by the electromagnetic action (aclosed state or an ON state). The second relay 12B has a configurationsame as the first relay 12A.

The diode D is connected in series to the second relay 12B between apair of common connection points K1 and K2 each of which is commonlyconnected to the first relay 12A and the second relay 12B. Specifically,the diode D is connected in series to the second relay 12B such that ananode side thereof is connected to the common connection point K1 and acathode side thereof is connected to the common connection point K2. Inother words, the diode D is connected to block the electric currentflowing in a charge direction that charges the assembled battery 11. Thediode D is one example of a rectifier component. The diode D is notconnected to the first relay 12A between the pair of common connectionpoints K1 and K2.

When the first relay 12A or the second relay 12B is in the closed state,a path of a current is formed between the assembled battery 11, thestarter 3, the in-vehicle device 4 and the alternator 5. Specifically,if at least the first relay 12A is in the closed state, a current path(hereinafter, referred to as a discharge path) is formed between theassembled battery 11, the starter 3, and the in-vehicle device 4 via thefirst relay 12A. This enables the electric power to be supplied from theassembled battery 11 to the starter 3 and the in-vehicle device 4. Acurrent path (hereinafter, referred to as a charge path) is formedbetween the assembled battery 11 and the alternator 5 via the firstrelay 12A. This enables the electric power to be supplied from thealternator 5 to the assembled battery 11.

If the first relay 12A is in the open state and the second relay 12B isin the closed state, the discharge path is formed between the assembledbattery 11, the starter 3, and the in-vehicle device 4 via the secondrelay 12B. This enables the electric power to be supplied from theassembled battery 11 to the starter 3 and the in-vehicle device 4. Thecharge path is formed between the assembled battery 11 and thealternator 5 via the second relay 12B. However, the diode D is connectedto block the current flowing in the charge direction that charges theassembled battery 11. Therefore, the electric power is not supplied fromthe alternator 5 to the assembled battery 11.

The first relay 12A and the second relay 12B may be arranged outside theelectric storage apparatus 1. The first relay 12A is one example of thefirst switch and the second relay 12B is one example of the secondswitch.

The BMS 13 includes a voltage detection circuit 21, the controller 22, acurrent detection circuit 23, and an equalization circuit 25. Thevoltage detection circuit 21 is one example of a voltage detector anddetects a voltage of each of the cells C1 to C4 independently andtransmits a detection result to the controller 22. The voltage detectioncircuit 21 may be configured to detect a voltage of the assembledbattery 11 as a whole. The current detection circuit 23 detects a chargecurrent and a discharge current flowing through the assembled battery 11(hereinafter, referred to as a charge/discharge current) and transmits adetection result to the controller 22.

The BMS 13 includes the voltage detection circuit 21 and the currentdetection circuit 23 and may further include various detectors (notillustrated) such as a temperature sensor that detects temperature ofthe assembled battery 11. The BMS 13 may monitor various conditions ofthe assembled battery 11 such as an internal resistance or a state ofcharge (hereinafter, simply referred to as a SOC) of the assembledbattery 11 based on a detection result of the detectors.

The controller 22 includes a central processing unit (hereinafter, CPU)22A, and a memory 22B. The memory 22B stores various programs forcontrolling operations of the controller 22 (including a program forperforming a secondary battery protection process that will be describedlater). The CPU 22A controls each part of the electric storage apparatus1 according to a program read from the memory 22B. The memory 22Bincludes a RAM and a ROM. The various programs may be stored in mediumsuch as the RAM or a non-volatile memory such as a CD-ROM, a hard discdevice, or a flash memory. The controller 22 is supplied with electricpower from the assembled battery 11 to be driven.

When receiving the open command signal from the controller 22, the firstrelay 12A mechanically opens the contact point (in the open state or theOFF state) by the electromagnetic action. When receiving the closecommand signal from the controller 22, the first relay 12A mechanicallycloses the contact point (in the closed state or the ON state) by theelectromagnetic action. The second relay 12B has a configuration same asthe first relay 12A.

The equalization circuit 25 substantially equalizes the voltages of thefour cells CN. Specifically, the equalization circuit 25 includes fourdischarge circuits HD1 to HD4 each of which is connected in parallel toeach of the cells C1 to C4. Each discharge circuit HD includes theswitching component 25A and a discharge resistance 25B that areconnected in series. The discharge circuit HD is one example of thedischarger.

The controller 22 provides the close command signal to the switchingcomponent 25A of each discharge circuit HD and makes the switchingcomponent 25A to be in the closed state. Accordingly, the controller 22discharges the electric power from the cells C1 to C4 via the dischargeresistance 25B to lower the voltage values of the cells C1 to C4. Thecells C1 to C4 are connected in parallel to the equalization circuit 25.When determining that it is not necessary to lower the voltage values ofthe cells C1 to C4, the controller 22 provides the open command signalto the switching component 25A of each discharge circuit HD and makesthe switching component 25A to be in the open state.

Lithium Iron Phosphate Secondary Battery

Problems that may be caused in charging a lithium iron phosphatesecondary battery will be described with reference to FIGS. 2 and 3. AnOCV-SOC curve P is illustrated by a solid line in FIG. 2. The OCV-SOCcurve P represents variation characteristics (correlation) between anopen circuit voltage (hereinafter, referred to as an OCV) and a SOC ofthe cell C. The OCV is a terminal voltage of the cell C in a stablestate. For example, the OCV is a terminal voltage of the cell C when thevoltage change amount of the cell C in a unit time period is a certainamount or less. The certain amount is previously determined based on aspec of the cell C or certain experiments. Data regarding the OCV-SOCcurve P is stored in the memory 22B.

As illustrated in FIG. 2, the graph illustrating relation of the SOC andthe OCV of the lithium iron phosphate secondary battery has a flatregion (a plateau region) where the change ratio of the OCV isrelatively small and a change region where the change ratio of the OCVis relatively great. The change ratio of the OCV represents a changeamount of the OCV in a unit change amount of the SOC. Specifically, theregion of the graph in FIG. 2 close to the SOC from 25% to 97% is theflat region where the change ratio of the OCV is relatively small, andthe region of the graph close to the SOC of 25% and less and the SOC of97% and more is the change region where the change ratio of the OCV isrelatively great.

The lithium iron phosphate secondary battery has the abovecharacteristics, and for example, if the SOC is close to 100%, thechange ratio of the OCV is extremely great, and therefore, even if theSOC slightly increases, the voltage of each cell CN promptly increasesand greatly exceeds the maximum charge voltage value. A secondarybattery protection process that will be described later is effectivelyperformed for the assembled battery 11 including the cells that areconnected in series.

If the SOC of each of the cells C1 to C4 varies, for example, the SOC ofthe cell C1 in FIG. 1 is 100%, the SOC of the cell C2 is 95%, the SOC ofthe cell C3 is 90%, and the SOC of the cell C4 is 80% and the assembledbattery 11 is charged with a constant voltage, a problem may be causedas illustrated in FIG. 3.

In the example illustrated in FIG. 3, the electric storage apparatus 1is charged with a constant voltage of 14.8 V. In the graph illustratedin an upper portion of FIG. 3, the vertical axis represents a chargevoltage (V) of the assembled battery 11 and the horizontal axisrepresents time (hr). In the graph illustrated in a middle portion ofFIG. 3, the vertical axis represents a charge current (A) of theassembled battery 11 and the horizontal axis represents time (hr). Inthe graph illustrated in a lower portion of FIG. 3, the vertical axisrepresents a cell voltage (V) of the cell C and the horizontal axisrepresents time (hr).

Even if the SOC of each of the cells C1 to C4 varies, the charger suchas the alternator 5 just charges the assembled battery 11 with aconstant voltage. The charger does not perform the constant voltagecharging with monitoring the cell voltage of each of the cells C1 to C4.Therefore, the variation in the SOC of the cells C1 to C4 will not beremoved. The MBS 13 includes the equalization circuit 25 to remove thevariation. Specifically, each discharge circuit HD of the equalizationcircuit 25 discharges electric power from each of the four cells CN tolower the voltage value of each of the four cells CN. This substantiallyequalizes the voltages of the four cells CN.

However, it takes predetermined time for the discharging via eachdischarge circuit HD of the equalization circuit 25. Therefore, forexample in FIG. 3, after the cell voltage of the cell C1 exceeds themaximum charge voltage value (for example, 4.0 V) that is determinedbased on a spec of the cell C1, the constant voltage charging isperformed. This is caused because the SOC of the cell C1 before startingthe constant voltage charging is in the change region.

The SOC of each of the cells C2 to C4 before starting the constantvoltage charging is in the plateau region. Therefore, even if theconstant voltage charging starts and the SOC increases, the OCV is lesslikely to change. However, the SOC of the cell C1 before starting theconstant voltage charging is in the change region. Therefore, if theconstant voltage charging for the cell C1 is started and the SOCincreases even slightly, the OCV increases rapidly. As a result, afterthe cell voltage of the cell C1 exceeds the maximum charge voltagevalue, the constant voltage charging is performed for the cell C1, andthis may deteriorate the cell C1.

Secondary Battery Protection Process

The controller 22 always performs a secondary battery protection processillustrated in FIG. 4 while being supplied with power source from theassembled battery 11.

The secondary battery protection process is performed so as not toperform the constant voltage charging for the assembled battery 11 in astate that the cell voltage of each cell C1 to C4 is greater than themaximum charge voltage value. Specifically, the controller 22 performsan initial process to make the first relay 12A to be a closed state andmake the second relay 12B to be an open state (S1). Accordingly, in anormal state, the charge/discharge current flows not via the diode D,and therefore, the heating by the diode D does not occur. The process ofS1 is an example of a first process.

Next, the controller 22 makes the switch components 25A of the dischargecircuits HD1 to HD4 (S2) to be in the open state. The process of S2 isan example of a stop process.

Next, the controller 22 initializes the number N of the Nth cell CN tobe one (S3) and detects a voltage value of the Nth cell CN (S4). Thecontroller 22 determines whether the voltage value of the Nth cell CNdetected in S4 is a balancer drive voltage threshold value (for example,3.6 V) or greater (S5) and determines whether the Nth cell CN is closeto an overcharge state (one example of an overcharge state that iscaused due to a current flowing in a reverse direction of the rectifiercomponent). By comparing the voltage value of the Nth cell CN and thebalancer drive voltage threshold value, the controller 22 determineswhether to drive the equalization circuit 25 and make the switchingcomponent 25A to be in the closed state.

If determining that the voltage value of the Nth cell CN is the balancerdrive voltage threshold value or greater (S5: YES), the controller 22determines that the Nth cell CN is close to the overcharge state andperforms an overcharge protection process illustrated in FIG. 5 (S6). Arange of voltages smaller than the balancer drive voltage thresholdvalue is an example of a reference range. The process of S5 is anexample of a process in which it is determined whether the electricstorage device is in a first state or a second state. A state in whichthe voltage value of the Nth cell CN is the balancer drive voltagethreshold value or greater is one example of the second state.

Overcharge Protection Process

The overcharge protection process is performed such that the Nth cell CNdoes not become in the overcharge state. In the overcharge protectionprocess, the controller 22 discharges electric power from the Nth cellCN via the discharge circuit HD of the equalization circuit 25.Specifically, the controller 22 makes the switch component 25A that isconnected in parallel to the Nth cell CN to be in the closed state(S21). The process of S21 is an example of a discharge process.

The controller 22 determines whether the voltage value of the Nth cellCN is a stable voltage threshold value (for example, 3.5 V) or smaller(S22). By performing the process of S22, the controller 22 determineswhether the electric power of the Nth cell CN is discharged via thedischarge circuit HD of the equalization circuit 25 and the voltagevalue of the Nth cell CN is lowered to be the stable voltage thresholdvalue that is a stable voltage.

When determining that the voltage value of the Nth cell CN is the stablevoltage threshold value or smaller (S22: YES), the controller 22 makesthe switch component 25A to be in the open state (S29) and terminatesthe overcharge protection process and proceeds to S9 in FIG. 4. Thecontroller 22 determines that the electric power is discharged from theNth cell CN via the discharge circuit HD of the equalization circuit 25and the voltage value of the Nth cell CN is lowered.

When determining that the voltage value of the Nth cell CN is greaterthan the stable voltage threshold value (S22: NO), the controller 22determines whether the voltage value of the Nth cell CN is theovercharge voltage threshold value (for example, 3.7 V) or greater (S23)to determine whether the Nth cell CN is further closer to the overchargestate. When the controller 22 determines that the voltage value of theNth cell CN is smaller than the overcharge voltage threshold value (S23:NO), the process returns to S22 to continue discharging the electricpower of the Nth cell CN only via the discharge circuit HD of theequalization circuit 25.

When the controller 22 determines that the voltage value of the Nth cellCN is the overcharge voltage threshold value or greater (S22: YES), thefollowing processes will be performed to continue discharging theelectric power from the Nth cell CN via the discharge circuit HD of theequalization circuit 25 and restrict the charging of the Nth cell CN. Ifthe electric power is discharged from the Nth cell CN only via thedischarge circuit HD of the equalization circuit 25, it takes long timeto discharge the electric power and it is difficult to lower the voltagevalue of the Nth cell CN quickly.

The controller 22 makes the second relay 12B to be in the closed state(S24) and makes the first relay 12A to be in the open state (S25). Theprocesses of S24 and S25 are examples of the second process.

As described before, the diode D is connected in series to the secondrelay 12B so as to block the current flowing to the assembled battery 11(one example of a current flowing in a reverse direction of therectifying component). Therefore, when the controller 22 performs theprocess of S25, the charge path formed by the first relay 12A betweenthe alternator 5 and the assembled battery 11 is disconnected and thisblocks the charge current flowing from the alternator 5 to the assembledbattery 11. Accordingly, the Nth cell CN is in a state that the chargingis not performed.

The diode D is connected to the second relay 12B such that the currentflows from the assembled battery 11 to the in-vehicle device 4.Therefore, as a result of the processes of S24 and S25, a discharge pathis formed by the second relay 12B between the in-vehicle device 4 andthe assembled battery 11, and accordingly, the discharge current flowsfrom the assembled battery 11 to the in-vehicle device 4 via thedischarge path. Therefore, the Nth cell is in a state that onlydischarging is performed.

The process of S24 is performed such that the discharge path between thein-vehicle device 4 and the assembled battery 11 is not disconnected fora moment. Hereinafter, the process will be described specifically withreference to FIG. 6. In a configuration illustrated in an upper portionof FIG. 6, the first relay 12A is in the closed state and the secondrelay 12B is in the open state (case 1), in a configuration illustratedin a middle portion of FIG. 6, the first relay 12A is in the closedstate and the second relay 12B is in the closed state (case 2), and in aconfiguration illustrated in a lower portion of FIG. 6, the first relay12A is in the open state and the second relay 12B is in the closed state(case 3). The engine 2, the starter 3, the voltage detection circuit 21and the current detection circuit 23 are not illustrated in FIG. 6.

In the case 1, the first relay 12A is in the closed state. Therefore,the current path is formed between the assembled battery 11 and each ofthe in-vehicle device 4 and the alternator 5, and the charge/dischargecurrent flows through the assembled battery 11 via the first relay 12A.

In the case 2, the diode D is connected in series to the second relay12B so as to block the current flowing to the assembled battery 11.Therefore, the charge current does not flow through the assembledbattery 11 via the second relay 12B.

The second relay 12B is connected in parallel to the first relay 12A,and the diode D is connected in series to the second relay 12B betweenthe pair of common connection points K1, K2 each of which is commonlyconnected to the first relay 12A and the second relay 12B. Therefore,the current path generated by the second relay 12B has a greatersynthesized component of a circuit resistance compared to a current pathformed by the first relay 12A, and accordingly, the discharge currentdoes not flow from the assembled battery 11 via the second relay 12B.Therefore, also in the case 2, the charge/discharge current flowsthrough the assembled battery 11 via the first relay 12A.

In the case 3, only the discharge path is formed by the second relay 12Band therefore, only the discharge current flows from the assembledbattery 11.

If the controller 22 shifts the condition of the electric storageapparatus 1 from the case 1 to the case 3 directly without going throughthe case 2, the discharge path between the in-vehicle device 4 and theassembled battery 11 may be disconnected temporally. For example, whenthe controller 22 provides the open command signal to the first relay12A and provides the close signal to the second relay 12B at the sametime, both of the first relay 12A and the second relay 12B are in theopen state for a moment. Therefore, the power supply from the assembledbattery 11 to the in-vehicle device 4 is temporally interrupted andaccordingly, jumpiness in the audio sound or flicker of the head lightmay occur or a vehicular control system such as an engine or braking maybecome unstable, for example.

The controller 22 shifts the condition of the electric storage apparatus1 from the case 1 to the case 3 with going through the case 2, andaccordingly, the short temporal disconnection of the discharge pathbetween the in-vehicle device 4 and the assembled battery 11 is lesslikely to occur.

After the process of S25, the controller 22 determines whether thevoltage value of the Nth cell CN is the stable voltage threshold valueor smaller (S26). The controller 22 determines whether the electricpower is discharged from the Nth cell CN and the voltage value of theNth cell CN is lowered by performing the process of S26.

When determining that the voltage value of the Nth cell CN is greaterthan the stable voltage threshold value (S26: NO), the controller 22waits. When determining that the voltage value of the Nth cell CN is thestable voltage threshold value or smaller (S26: YES), the controller 22determines that the electric power is discharged from the Nth cell andthe voltage value of the Nth cell CN is lowered, and returns theassembled battery 11 to be in a chargeable/dischargeable state.Specifically, the controller 22 makes the first relay 12A to be in theclosed state (S27) and makes the second relay 12B to be in the openstate (S28).

The controller 22 performs the process of S28 after performing theprocess of S27 to prevent the short disconnection of the discharge pathbetween the in-vehicle device 4 and the assembled battery 11 asdescribed before. The process of S27 and the process of S28 are examplesof the first process.

The controller 22 terminates the discharging from the cell CN via theequalization circuit 25. Specifically, the controller 22 makes the Nthswitch component 25A to be in the open state (S29). The Nth switchcomponent 25A is connected in parallel to the Nth cell CN. Accordingly,the controller 22 terminates the overcharge protection process and theprocess proceeds to S9 in FIG. 4. The process of S29 is an example ofthe stop process.

When determining that the voltage of the electric storage device is inthe reference range, the controller 22 performs discharging by thedischarger and when determining that the voltage of the electric storagedevice is not in the reference range, the controller 22 performs thesecond process.

When determining that the voltage value of the Nth cell CN is smallerthan the balancer drive voltage threshold value (S5: NO), the controller22 determines whether the voltage value of the Nth cell CN is anoverdischarge voltage threshold value (for example, 3.25 V) or smaller(S7) to determine whether the Nth cell CN becomes closer to theovercharge state. By comparing the voltage value of the Nth cell CN andthe overcharge voltage threshold value, the controller 22 determineswhether to perform an overcharge protection process. When determiningthat the voltage value of the Nth cell CN is the overcharge voltagethreshold value or smaller (S7: YES), the controller 22 performs theovercharge protection process illustrated in FIG. 7 (S8).

A range of voltage values greater than the overcharge voltage thresholdvalue is an example of the reference range. The process of S7 is anexample of the process of determining whether the voltage value is inthe reference range, and the state in which the voltage value of the Nthcell CN is the overdischarge voltage threshold value or smaller is anexample of the third state.

Overdischarge Protection Process

The overdischarge protection process is performed such that the Nth celldoes not become in the overdischarge state (one example of theoverdischarge state caused by a current flowing in a forward directionof the rectifier component). Specifically, in the overdischargeprotection process, the controller 22 measures elapsed time from theexecution of the overdischarge protection process and determines whetherthe elapsed time reaches reference time (for example, thirty seconds)(S31). When determining that the elapsed time does not reach thereference time (S31: NO), the controller 22 determines whether thevoltage value of the Nth cell CN is the overdischarge voltage thresholdvalue or smaller (S32).

When the controller 22 determines that the voltage value of the Nth cellCN is greater than the overdischarge voltage threshold value (S32: NO),the voltage value of the Nth cell CN is lowered to be the overdischargethreshold value or smaller due to temporal voltage dropping, andtherefore, the controller 22 terminates the overdischarge protectionprocess. The process proceeds to S9 in FIG. 4.

When the controller 22 determines that the voltage value of the Nth cellCN is the overdischarge threshold value or smaller (S32: YES), theprocess returns to S31.

In S31, when determining that the elapsed time reaches the referencetime (S31: YES), the controller 22 makes the first relay 12A to be inthe open state (S33) and disconnects the discharge path between thein-vehicle device 4 and the assembled battery 11. This stops thedischarge current (one example of current flowing in the forwarddirection of the rectifier component) flowing from the assembled battery11.

After the process of S33, the controller 22 determines whether toreceive a recovery command (S34). The recovery command is transmitted tothe electric storage apparatus 1 from an electronic control unit of avehicle (hereinafter, referred to as an ECU) according to driver'sactions such as moving an ignition switch to an ignition position orpressing on an accelerator of a vehicle that is in an idling stop state,for example.

When determining that the controller 22 does not receive the recoverycommand (S34: NO), the controller 22 waits. When determining that thecontroller receives the recovery command (S34: YES), the controllerdetermines whether the voltage value of the Nth cell CN is a batteryexchange voltage threshold value (for example, 2.8 V) or greater (S35).The controller 22 determines whether the Nth cell CN is in theoverdishcarge state by comparing the voltage value of the Nth cell CNand the battery exchange voltage threshold value. When determining thatthe voltage value of the Nth cell CN is smaller than the batteryexchange voltage threshold value (S35: NO), the controller 22 determinesthat the Nth cell is in the overdischarge state and stores in the memory22B a flag representing that the electric storage apparatus 1 isrequired to be exchanged (S36). Then, the controller 22 terminates theoverdischarge protection process and the process proceeds to S9 in FIG.4.

When determining that the Nth cell CN is in the overdischarge state andit is required to exchange the electric storage apparatus 1, thecontroller 22 may perform an error process and output an inform signalto an external device such as the ECU, for example. For example, theinform signal represents that the electric storage apparatus 1 isrequired to be exchanged.

When determining that the voltage value of the Nth cell CN is thebattery exchange voltage threshold value or greater (S35: YES), thecontroller 22 determines that the Nth cell CN is not in theoverdischarge state and returns the assembled battery 11 to be in achargeable/dischargeable state. Specifically, the controller 22 makesthe first relay 12A to be in the closed state (S37) and terminates theoverdischarge protection process, and the process proceeds to S9 in FIG.4. The overdischarge protection process is an example of the thirdprocess and the process of S37 is an example of the first process.

The controller 22 determines whether the number N of the Nth cell CNreaches a total number (=4) (S9). When the controller 22 determines thatthe number N of the Nth cell CN reaches the total number (S9: YES), theprocess returns to S3 and the controller 22 performs the processes afterS3 again regarding the first cell C1. On the other hand, whendetermining that the number N of the nth cell CN does not reach thetotal number (S9: NO), the controller 22 adds one to the number N of theNth cell CN (S10) and the process returns to S4 and the processes willbe performed from S4.

Effects of this Embodiment

According to this embodiment, the electric storage apparatus 1 includesthe first relay 12A, the second relay 12B that is connected in parallelto the first relay 12A, and the diode D that is connected in series tothe second relay 12B between the pair of common connection points K1, K2that are commonly connected to the first relay 12A and the second relay12B. In the electric storage apparatus 1, the controller 22 performs theovercharge protection process and the overdischarge protection process.Specifically, when performing the overdischarge protection process, thecontroller 22 makes the first relay 12A and the second relay 12B to bein the open state. Accordingly, the assembled battery 11 is protectedfrom becoming in the overdischarge state. When performing the overchargeprotection process, the controller 22 makes the second relay 12B to bein the closed state, and then makes the first relay 12A to be in theopen state. Accordingly, the discharge path from the assembled battery11 is maintained with protecting the assembled battery 11 from becomingin the overcharge state. When the assembled battery 11 is in a normalstate, the second relay 12B becomes in the open state and the firstrelay 12A becomes in the closed state to generate a current path betweenthe assembled battery 11 and the in-vehicle device 4. Thecharge/discharge current flows in the current path, and therefore,heating is less likely to occur on the current path compared to aconfiguration in which the rectifier component such as the diode D isarranged on the current path.

Other Embodiments

The present invention is not limited to the embodiments described aboveand illustrated in the drawings. The following various embodiments arealso included in the technical scope of the present invention.

In the above embodiment, the controller 22 includes one CPU 22A and thememory 22B. However, the controller may not be limited thereto and mayinclude a plurality of CPUs or include a hardware circuit such as anapplication specific integrated circuit (ASIC) or may include both of ahardware circuit and a CPU. For example, a part or all of process stepsof the secondary battery protection process may be performed by separateCPUs or hardware circuits. The execution order of the process steps maybe altered if necessary.

In the above embodiment, examples of the switch include the first relay12A and the second relay 12B of the contact type. However, the switch isnot limited thereto but may be a semiconductor component such as abipolar transistor and MOSFET or may be a relay of a normal closed type.The relay of a normal closed type is normally in the closed state andbecomes in the open state only when receiving an open command signal.The switching component 25A of the discharge circuit HD (one example ofthe discharger) may have a configuration same as the modifications ofthe first relay 12A and the second relay 12B described above.

In the above embodiment, the assembled battery 11 including multiplecells that are connected in series is used as an example of the electricstorage device. However, the electric storage device is not limitedthereto but may be an electric cell including one cell or may be oneincluding multiple cells that are connected to each other in parallel.The electric storage device may include two, three, five or more cellsand the number of cells included in the electric storage device may bealtered if necessary. The electric storage device does not necessarilyinclude the iron phosphate-based material as the positive electrodeactive material but may include at least an iron component. The electricstorage device does not necessarily include the negative electrodeformed by a graphite-based material. The electric storage device may beother secondary batteries such as a lead-acid battery, a manganese-typelithium-ion battery. The electric storage device is not necessarily asecondary battery but may be a capacitor or an electric double layercapacitor.

In the above embodiment, the electric storage device includes the ironphosphate-based material as the positive electrode active material.However, a small amount of a specific lithium compound may be mixed withthe iron phosphate-based material and the obtained mixture may be usedas the positive electrode active material. The specific lithium compoundhas an OCV greater than the OCV of the iron phosphate-based material inthe plateau region. Examples of the specific lithium compound preferablyinclude LiCo2, LiNiO2 of a nickel type, LiMn2O4 of a manganese type, andLi—Co—Ni—Mn type oxide. A ratio of the specific lithium compound to theiron phosphate-based material is preferably five percent by weight orless. Accordingly, the OCV change ratio in the SOC range of the electricstorage device close to 100% becomes small and the range of the OCV-SOCcurve P of the electric storage device having great change is reducedand therefore, the SOC is easily estimated. This makes charge/dischargecontrol to be performed easily. The overcharge or overdischarge is lesslikely to be caused in the electric storage device.

In the above embodiment, the two relays including the first relay 12Aand the second relay 12B are connected to each other in parallel.However, a three-points switching relay KR illustrated in FIG. 8 may beused. The three-points switching relay KR includes three contact pointsST1 to ST3 and a contact point TP that is connected to the assembledbattery 11. The contact point ST1 is connected to a circuit that isconnected to the diode D, the contact point ST2 is connected to acircuit that is not connected to the diode D, and the contact point ST3is not connected to any circuit. In case of using the three-pointsswitching relay KR, the controller 22 provides a switch command signalto the three-points switching relay KR and connects one of the threecontact points ST1, ST2, ST3 of the three-points switching relay KR tothe contact point TP. The three-points switching relay KR including themultiple contact points ST1 to ST3 is an example of switches.

In the above embodiment, the diode D is used as an example of therectifier component. However, the rectifier component may be asemiconductor component such as MOSFET that is connected to the diode,for example. The rectifier component may be a circuit providing afunction similar to that of the diode.

In the above embodiment, the voltage detection circuit 21 detects thevoltage of each of the cells C1 to C4 independently and transmits thedetection result to the controller 22. However, the ECU may detect thevoltage of each of the cells C1 to C4 independently and the BMS 13 mayreceive a signal from the ECU.

In the above embodiment, the alternator 5 does not include a controlcircuit for the charge control. However, the alternator 5 may include acontrol circuit for the charge control. The charger may not benecessarily arranged in a vehicle like the alternator 5 but may be anexternal charger such as a charging stand or a battery charger.

In the above embodiment, the circuit switch 12 is arranged between theassembled battery 11 and the in-vehicle device 4 and between theassembled battery 11 and the alternator 5. However, the circuit switch12 may be arranged between a battery plus terminal BP and the alternator5 or may be arranged between the battery plus terminal BP and thein-vehicle device 4.

In the above embodiment, the voltage detection circuit 21 detects thevoltage of each of the cells C1 to C4 independently and transmits thedetection result to the controller 22. However, the voltage detectioncircuit 21 may detect a voltage of the whole assembled battery 11. Inthe configuration where the voltage detection circuit 21 detects avoltage of the whole assembled battery 11, the processes of S3, S9, S10in FIG. 4 are not necessary and the balancer drive voltage thresholdvalue, the overdischarge voltage threshold value used in the process inFIG. 4, the stable voltage threshold value, the overcharge voltagethreshold value used in the process in FIG. 5, and the battery exchangevoltage threshold value used in the process in FIG. 7 may be alteredfrom the threshold value of each of the cells C1 to C4 to the thresholdvalue of the whole assembled battery 11. For example, each of thethreshold values may be quadrupled or the plateau voltage may be tripledand the overcharge threshold value of one of the cells C1 to C4 may beadded to the tripled plateau voltage to obtain the threshold value ofthe whole assembled battery 11. One example of a formula of adding theovercharge threshold value of one of the cells C1 to C4 to the tripledplateau voltage is as follows.Plateau voltage (3.3 V)*3+overcharge threshold value (4.0V)*1=approximately 14.0 V (threshold value of the whole assembledbattery 11)Only the cell C that has a maximum voltage may be connected to thedischarge circuit HD.

In the above embodiment, the balancer drive voltage threshold value andthe overdischarge voltage threshold value are examples of the thresholdvalue that determines the reference range. The balancer drive voltagethreshold value is smaller than a lower limit value that causes each ofthe cells C1 to C4 to be in the overcharge state, and this prevents eachof the cells C1 to C4 from becoming in the overcharge state. Theoverdischarge voltage threshold value is greater than an upper limitvalue that causes each of the cells C1 to C4 to be in the overdischargestate, and this prevents each of the cells C1 to C4 from becoming in theoverdischarge state. However, the balancer drive voltage threshold valuemay be substantially equal to the lower limit value that causes eachcell C1 to C4 to be in the overcharge state and the overdischargevoltage threshold value may be substantially equal to the upper limitvalue that causes each cell C1 to C4 to be in the overdischarge state.Accordingly, even if the cell C1 to C4 becomes in the overcharge stateor the overdischarge state, the cell C1 to C4 is not continuously keptin that state.

In the above embodiment, the controller 22 detects a cell voltage ofeach of the four cells CN one by one and compares the detected voltageand the corresponding threshold value and performs the overchargeprotection process and the overdischarge protection process. However,the controller 22 may detect the cell voltages of all of the four cellsCN first and compare the cell voltages and the corresponding thresholdvalue sequentially from a greatest one of the detected cell voltages andperform the overcharge protection process.

In the above embodiment, when determining that the voltage of theelectric storage device is in the reference range, the controller 22controls the discharger to perform the discharge process. Whendetermining that the voltage of the electric storage device is not inthe reference range, the controller 22 performs the second process.However, when determining that the voltage of the electric storagedevice is not in the reference range, the controller 22 may perform thesecond process and thereafter, when determining that the voltage of theelectric storage device is in the reference range, the controller 22 maycontrol the discharger to perform the discharge process.

In the above embodiment, when the assembled battery 11 is in the voltageabnormal state such as the overcharge state or the overdischarge state,it is considered as the abnormal state of the assembled battery 11.However, a temperature abnormal state or a current abnormal state may beconsidered as the abnormal state of the assembled battery 11. When adetection result of temperature of the assembled battery 11 detected bya temperature sensor is higher than a reference threshold value, theassembled battery 11 is in the temperature abnormal state. When acharge/discharge current flowing through the assembled battery 11 thatis detected by the current detection circuit 23 is greater than areference threshold value, the assembled battery 11 is in the currentabnormal state.

The invention claimed is:
 1. An electric storage device protectionapparatus comprising: switches arranged between an electric device andan electric storage device and connected in parallel to each other, andeach of which being configured to be switched to be in an open state anda closed state; a rectifier component connected in series to one of theswitches between a pair of common connection points of the switches; anda controller configured to: perform a first process to make the one ofthe switches that is connected to the rectifier component to be in theopen state when determining that the electric storage device is in afirst state where a voltage of the electric storage device is within areference range; and perform a second process to make the one of theswitches that is connected to the rectifier component to be in theclosed state and make another one of the switches to be in the openstate when determining that the electric storage device is in a secondstate where a voltage of the electric storage device becomes outside thereference range due to a current flowing in a reverse direction of therectifier component.
 2. The electric storage device protection apparatusaccording to claim 1, wherein the switches include a first switch and asecond switch, the first switch being arranged between the electricdevice and the electric storage device and switched between the openstate and the closed state, and the second switch being connected inparallel to the first switch between the electric device and theelectric storage device and switched between the open state and theclosed state, wherein the rectifier component is connected in series tothe second switch between the pair of common connection points of thefirst switch and the second switch, and wherein the controller isfurther configured to: make at least the first switch to be in theclosed state when determining that the electric storage device is in thefirst state; and make the first switch to be in the open state and makethe second switch to be in the closed state when determining that theelectric storage device is in the second state.
 3. The electric storagedevice protection apparatus according to claim 2, wherein the electricdevice includes a charger and a load, and wherein the first switch, thesecond switch, and the rectifier component are connected to a commoncurrent path commonly arranged between the charger and the electricstorage device and between the load and the electric storage device. 4.The electric storage device protection apparatus according to claim 3,wherein the controller is configured to make the second switch to be inthe closed state first and thereafter make the first switch to be in theopen state in the second process.
 5. The electric storage deviceprotection apparatus according to claim 3, wherein the controller isfurther configured to: determine whether the electric storage device isin a third state where the voltage of the electric storage devicebecomes outside the reference range due to a current flowing in aforward direction of the rectifier component; and perform a thirdprocess to make the first switch and the second switch to be in the openstate when determining that the electric storage device is in the thirdstate.
 6. The electric storage device protection apparatus according toclaim 2, further comprising a discharger connected in parallel to theelectric storage device and configured to be switched between adischarge state where electric power is discharged from the electricstorage device and a stop state where discharge is stopped, wherein therectifier component is connected to the second switch so as to block acurrent flow that charges the electric storage device, and wherein thecontroller is further configured to: perform the stop process to makethe discharger in the stop state when determining that the electricstorage device is in the first state; and perform the discharge processto make the discharger in the discharge state when determining that theelectric storage device is in the second state.
 7. The electric storagedevice protection apparatus according to claim 2, wherein the controlleris further configured to make the second switch to be in the open statein the first process.
 8. The electric storage device protectionapparatus according to claim 2, wherein the first switch is directlyconnected to the pair of common connection points, and wherein thesecond switch is directly connected to the rectifier component and oneof the pair of common connection points.
 9. An electric storageapparatus comprising: an electric storage device; and the electricstorage device protection apparatus according to claim
 1. 10. Theelectric storage apparatus according to claim 9, wherein the electricstorage device includes a positive electrode material including an ironphosphate-based material as a positive electrode active material. 11.The electric storage apparatus according to claim 9, wherein theelectric storage device includes a positive electrode material includinga lithium compound containing an iron component and a specific lithiumcompound as a positive electrode active material, the specific lithiumcompound providing an open circuit voltage greater than an open circuitvoltage provided by the lithium compound containing the iron compoundincluded as the positive electrode active material, the open circuitvoltage being obtained in a flat region where a change rate of the opencircuit voltage per a state of charge unit is small.
 12. A starterbattery comprising the electric storage apparatus according to claim 9.13. The starter battery according to claim 12, wherein the electricstorage device includes four lithium ion battery cells that areconnected in series to each other.
 14. The starter battery according toclaim 12, wherein the electric storage device is built into the starterbattery.
 15. The starter battery according to claim 12, wherein therectifier component comprises a diode connected in series to the one ofthe switches such that an anode side of the diode is coupled to one ofthe pair of common connection points of the switches and a cathode sideof the diode is coupled to the one of the switches.
 16. The electricstorage device protection apparatus according to claim 1, wherein thefirst switch is directly coupled to the pair of common connectionpoints.
 17. The electric storage device protection apparatus accordingto claim 16, wherein the second switch is directly coupled to therectifier component and one of the pair of common connection points. 18.A method of protecting an electric storage device in an electric storagedevice protection apparatus including switches arranged between anelectric device and an electric storage device and connected in parallelto each other and configured to be switched between an open state and aclosed state, and a rectifier component connected in series to one ofthe switches between a pair of common connection points of the switches,the method comprising: performing a first process to make the one of theswitches that is connected to the rectifier component to be in the openstate when determining that the electric storage device is in a firststate where a voltage of the electric storage device is within areference range; and performing a second process to make the one of theswitches that is connected to the rectifier component to be in theclosed state and make another one of the switches to be in the openstate when determining that the electric storage device in a secondstate where a voltage of the electric storage device becomes outside thereference range due to a current flowing in a reverse direction of therectifier component.
 19. The method according to claim 18, wherein therectifier component comprises a diode connected in series to the one ofthe switches such that an anode side of the diode is coupled to one ofthe pair of common connection points of the switches and a cathode sideof the diode is coupled to the one of the switches.
 20. The methodaccording to claim 18, wherein the first switch is directly coupled tothe pair of common connection points, and wherein the second switch isdirectly coupled to the rectifier component and one of the pair ofcommon connection points.